Problems needing attention in the most popular UV

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Problems needing attention in UV offset printing process

with the continuous improvement of people's requirements for packaging and decoration, UV printing has been more and more widely used because the ink does not contain volatile solvents. It can be quickly solidified on the surface of non absorbable substrate, high brightness and friction resistance of prints. Especially in cigarette bag decoration. At present, many medium and high-end cigarette packs are decorated by using UV offset printing on bright gold, silver paperboard or laser paper, printing rich levels of continuous adjustable patterns, polishing with UV varnish, and partial hollowing for embossing. Due to the high brightness of paper and UV varnish, the embossing part looks very eye-catching, which can achieve the effect of bronzing and silver ironing. After adopting this technology, the whole decoration looks very high-grade and easy to attract the attention of consumers. In the whole printing process, the mastery of UV offset printing process is very important and difficult, and it is also a link where product quality is prone to problems. How to improve the operation level of UV offset printing process and product quality in the production process? Next, the author talks about several issues that need to be paid attention to and mastered according to his work experience. UV offset printing requirements for printing plates, cots and blanket

due to the active monomer diluents and photoinitiators contained in UV offset printing inks, they can decompose the dots on the ordinary rubber i~ops plates, so that the print resistance of the printing plates is significantly reduced, so a special UV offset PS version must be selected for UV offset printing. However, the active monomer diluent in UV offset printing ink will saturate ordinary offset rollers and blanket during the printing process. The result will cause two printing failures: one is ink failure. Ordinary cots, especially new cots and blanket, absorb a large amount of this active monomer diluent in the ink at the early stage of operation, which directly destroys the fluidity of the ink and makes the ink dry The viscosity increases and cannot be inked normally. The active monomer in the ink film decreases, and the ink polymerization crosslinking component is insufficient. When the ink film is irradiated and cured by UV lamp, it will cause incomplete curing of the ink film, and the printing product is not resistant to friction: the second is the failure of the rubber roller and blanket. The active monomer diluent in the UV offset printing ink will cause the expansion and swelling of the general rubber roller and blanket, and short-term printing will cause expansion and deformation. Surface vitrification The dirt on the printed matter makes the printing unable to proceed normally. With the extension of printing time, peeling or surface fragmentation will occur when the expansion is more serious. Therefore, special UV cots and UV blanket or UV, ordinary dual-purpose cots and blanket must also be selected for UV offset printing

determination of UV offset printing color sequence

in ordinary offset printing process, the printing color sequence of ink is mainly determined by the following aspects:

1. The type of machine: monochrome, two-color or multi-color. This determines whether the overprint method of ink in the printing process is wet press dry or wet press wet

2. The content of the original determines the main color of the picture and the amount of various colors in the layout

3. the quality of paper determines the thickness of the first color ink layer, the deformation of paper and the gloss of printed matter

4. The difference of ink determines its color deviation, gray scale, color efficiency, and the matching of viscosity, transparency and coloring power

In addition to the above factors, the determination of the color sequence of UV offset printing is mainly determined by the curing performance of the ink. The curing of ordinary offset printing ink is the combination of oxidation conjunctiva and penetration curing, and the curing performance of all colors of ink is basically the same. The curing of UV offset printing ink is through the use of U (1) high-performance carbon fiber composites, which still needs several years of exploration and research and development. Due to the different absorption of UV light by various pigments in the ink, the curing degree of different colors of inks is also different. From the perspective of the penetration of UV light into pigments, magenta transmittance is 50% - 60%, yellow transmittance is 20% - 30%, cyan transmittance is 8% - 20%, and black transmittance is 10% - 12%. While white ink reflects 10, safe, reliable, and helps most of the UV light, and the transmittance is lower. Due to the different transmittance of various inks to UV light, some inks can cure while others cannot under the same UV light with the same power and at the same time. Therefore, in the arrangement of UV offset printing color sequence, we should mainly consider the curing of ink. Print the ink that is not easy to cure first, so that they can get more UV light irradiation, and then print the ink that is easy to cure. That is, the printing color sequence is: White Black green yellow magenta, so that the color preparation ink can be completely cured at the end of printing

in addition, two complementary inks can be used to adjust when printing black ink to accelerate the curing of the ink. The author's company adopted this method when printing a cigarette label, and achieved good results. This cigarette label (see the real object) is printed with horizontal light column laser paper. The main color is full page red. There is a leak in the red pattern on its side. The white ink is used as the bottom of the leak, and the black bar code is printed on the white ink. The white ink is used as the first color for printing. The black ink is used as the second color for printing. It is found that the ink is not cured completely and the bar code is weak. We mix the black ink used for printing with red ink and green ink, and then add a small amount of black ink: and add a small amount of red ink to the white ink (because the environmental color is red. As long as the amount of red ink in the white ink is appropriate, the effect on the hue cannot be observed by the naked eye). When printing with the newly prepared ink, the white ink and black ink solidify more thoroughly, and the printed bar code is full and clear

therefore, understanding the differences in the curing of UV offset color preparation inks, reasonably arranging the printing color sequence, and scientifically using complementary colors for inking are important methods to improve the balance of water and ink in UV offset printing process and realize product quality

realization of water ink balance in UV offset printing process

in offset printing process, the control of water ink balance is very important. Whether it is properly regulated directly affects the quality of products. Ordinary offset lithography uses the principle that water is polar and ink is non-polar. The two are immiscible, so that the ink and water can maintain a balanced relationship on the same page to realize the transfer of image points. On the printing plate, ink and water exist at the same time and must adapt to each other. Neither side can exceed the limit range and force the other side to develop in the opposite direction. The purpose of maintaining the balance of ink and water is to maintain the maximum ink load of graphics and texts, make the ink bright, clear, complete and full, and keep the blank area clean and tidy in the process of ink and water adapting to each other. In UV offset printing, the ink shows weak polarity and the substrate has poor water absorption, so the ink is easier to emulsify and the water black balance is more difficult to achieve. According to the working experience, the author believes that in order to better realize the balance of ink and water in UV offset printing process, we need to start from the following aspects:

1 several parameters of fountain solution should be well controlled. The temperature is between 4 and 9. C. The pH value is 5.5 ~ 6.3. The concentration of isopropanol is about 15%. After these parameters are controlled, the amount of fountain solution can be reduced and the emulsification of ink can be reduced

2. The selection of printing plate should be appropriate. It is best to use the special PS version of UV. The printing plate should have a solid graphic and blank foundation. The sand holes on the surface of the printing plate should be kept uniform and fine. It has a certain structural strength, so that ink and water have good adsorption

3. the operation process should be standardized. The pressure between the drum, ink roller and water roller should be well controlled. During printing, check the moisture of the printing sample and the layout frequently. Stir the ink in the ink bucket frequently to keep the printing pressure stable. The machine speed is stable. The temperature and humidity in the workshop are stable, so as to avoid the emulsification caused by the change of the nature of the ink

4. Realize the printing method of "thick ink and small water". At the beginning of printing, the ink volume and water volume should be small. Then the use of harmful solvents such as benzene, toluene and 2 toluene can be reduced by 120000 tons/year, and the ink volume and water volume can be gradually increased as needed. When it is found that the ink is emulsified, the emulsified ink should be scraped clean. Add eight new inks again for printing until it reaches the printing state of "low ink consistency and water". This is because the ink viscosity is large. That is, the cohesion of the ink increases. Accordingly, the adhesion between the ink molecules is enhanced. Thus, the water resistance of the ink is improved, the ratio of water in the ink is reduced, and the emulsification value of the ink is reduced, so as to ensure that the printed products are bright in color, thick in ink layer, clear and full

All these affect the safety of modern residents

in a word, UV offset printing process is difficult to master, so we must carefully observe and summarize it in our work, and master some necessary basic theoretical knowledge. When solving process problems, we should combine theory and experience, and compare it with the methods to solve ordinary offset printing process problems, so as to find out the similarities and differences. In this way, when solving process problems, we will have broader ideas and more appropriate methods, Will also print higher quality products

Author: Ma falai Zhengzhou Golden Leaf Printing Co., Ltd.

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